This invention relates to novel cyclopropanecarboxylic acid esters of 3-coumaranol, and derivatives thereof, as well as insecticidal compositions containing said esters as an essential active ingredient.
Current trends in the chemical control of insects call for inherently safer materials which degrade very rapidly to non-toxic substances once their purpose is accomplished. The safety of the widely used chlorinated hydrocarbons, notably DDT, is currently under question largely because of their poor biodegradability and concomitant persistence. Accordingly, there is a great demand for alternative broad spectrum insecticides which are suitable for the high volume usage entailed in agricultural applications. At the same time it is desirable for new insecticides to exhibit a low order of toxicity to warm-blooded animals. Of the several insecticidal classes which demonstrate low mammalian toxicity and good biodegradability, it has long been recognized that pyrethrum, a naturally-occurring insecticidal mixture, possesses these desirable properties. In addition to the safety advantages, this natural mixture causes rapid knock-down and kill of a broad spectrum of insects; however, it is unstable to light, air, and heat, and is very expensive. The most active component of pyrethrum is pyrethrin I and a number of analogous compounds have been proposed for insecticidal use. Allethrim, a typical synthetic pyrethrin-like insecticide, while more stable to light and heat than pyrethrum, is nevertheless expensive, a defect which is compounded by the fact that this substance is not appreciably synergized by the low cost synergizing agents such as piperonyl butoxide which are typically used in insecticidal compositions. Because of instability, high cost and limited supply, the use of pyrethrum and pyrethrin-like insecticides in agricultural applications has been precluded or seriously limited.
At the same time, it is well known that certain insects, in time, become immune to the insecticidal properties of various chemical agents. To be efficient, an insecticide should be able to resist detoxification by the insect. While biological mechanisms whereby insects are capable of detoxifying the various types of insecticidal compounds are not fully understood, it is possible that, as with other biological systems, insects may in time develop new biochemical processes capable of detoxifying any particular insecticidal compound. In any event, it is desirable to have included in the insecticidal armamentarium compounds which can be utilized once a given class of insects is found no longer to respond to conventional insecticidal compounds.
Many prior art insecticidal esters differ from one another and from the natural pyrethrin I esters by virtue of synthetic modifications in the alcohol moiety of the ester. Other synthetic insecticides are pyrethrin-like esters modified in the acid portion of the ester molecule. For example, the applications of Fanta, entitled "INSECTICIDAL ESTERS OF 3-(2,2-TETRAMETHYLENE ETHENYL)-2,2-DIMETHYLCYCLOPROPANECARBOXYLIC ACID," Ser. No. 23,513, filed Mar. 17, 1970 (now U.S. Pat. No. 3,679,667, issued July 25, 1972); NOVEL ESTERS OF CHRYSANTHEMIC ACID", Ser. No. 2,443, filed Jan. 12, 1970 (now abandoned); the copending application of Crawford, entitled "INSECTICIDAL ESTERS OF 1-ACENAPHTHENOL", Ser. No. 198,434, filed Nov. 12, 1971, and now U.S. Pat. No. 3,840,584, issued Oct. 8, 1974; and U.S. Pat. No. 3,465,007, Sept. 2, 1969, to M. Elliott, all relate to various synthetic insecticidal esters of the pyrethrum type. It has now been discovered that 3-coumaranol, and the various derivatives thereof, can be used in conjunction with cyclopropanecarboxylic acids to provide insecticidal esters of the pyrethrum type.
It is therefore an object of this invention to provide novel insecticidal 3-coumaranol esters of cyclopropanecarboxylic acids which are biodegradable, effect rapid knock-down and kill of a broad spectrum of insects, possess low mammalian toxicity and are less susceptible to detoxification by insects than is pyrethrum. This and other objects are obtained by the present invention as will become apparent from the following disclosure.